What is known as a heads-up display (HUD) is a display system in which information is projected into the field of vision of a user, for example the driver of a car or the pilot of an airplane. Pilots have had such systems since the 1940s, when they were known as reflex visors.
A heads-up display generally comprises a display device and an optical device which cooperate with what is known as a combiner. The display device generates an image from which the optical device, comprising for example a lens and a concave mirror, generates a virtual image which the driver or pilot views in a reflective, transparent screen: the combiner. The combiner therefore superimposes on the virtual image the environmental information appearing through the combiner.
If a heads-up display is installed in a motor vehicle, the windscreen of the motor vehicle may be used as the combiner.
For relatively good readability of the virtual image, the display device should generate not only a sufficiently bright image but also, if possible, a color image.
Published European application for patent EP 1 143 288 A1 discloses a heads-up display in which the light from a light source is transmitted through a liquid crystal display (LCD) screen and the image which may be seen on the liquid crystal display screen is projected on the windscreen of a motor vehicle as a virtual image. The light source comprises a plurality of red, blue and green light-emitting diodes disposed on a common carrier.
Published European application for patent EP 0 570 037 A1 discloses a further heads-up display comprising a monochrome or a polychrome display device.